[Patch net-next v2 3/3] net_sched: implement ->change_tx_queue_len() for pfifo_fast

[Cong Wang <xiyou.wangcong@gmail.com>]

pfifo_fast used to drop based on qdisc_dev(qdisc)->tx_queue_len,
so we have to resize skb array when we change tx_queue_len.

Other qdiscs which read tx_queue_len are fine because they
all save it to sch->limit or somewhere else in qdisc during init.
They don't have to implement this, it is nicer if they do so
that users don't have to re-configure qdisc after changing
tx_queue_len.

Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/sched/sch_generic.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 08f9fa27e06e..d7b82c379617 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -763,6 +763,22 @@ static void pfifo_fast_destroy(struct Qdisc *sch)
 	}
 }
 
+static int pfifo_fast_change_tx_queue_len(struct Qdisc *sch, unsigned int new_len)
+{
+	struct pfifo_fast_priv *priv = qdisc_priv(sch);
+	int ret = 0, prio;
+
+	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
+		struct skb_array *q = band2list(priv, prio);
+
+		ret = skb_array_resize(q, new_len, GFP_KERNEL);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
 struct Qdisc_ops pfifo_fast_ops __read_mostly = {
 	.id		=	"pfifo_fast",
 	.priv_size	=	sizeof(struct pfifo_fast_priv),
@@ -773,6 +789,7 @@ struct Qdisc_ops pfifo_fast_ops __read_mostly = {
 	.destroy	=	pfifo_fast_destroy,
 	.reset		=	pfifo_fast_reset,
 	.dump		=	pfifo_fast_dump,
+	.change_tx_queue_len =  pfifo_fast_change_tx_queue_len,
 	.owner		=	THIS_MODULE,
 	.static_flags	=	TCQ_F_NOLOCK | TCQ_F_CPUSTATS,
 };
-- 
2.13.0